This invention relates to an adjustment of an intake air volume under a control of a throttle opening degree in an internal combustion engine provided with a throttle opening degree control means for use in controlling a driving of a throttle valve.
In an internal combustion engine provided with this throttle opening degree control means, a target throttle opening degree is set mainly in response to an operating amount of accelerator such as a pressing amount of an accelerator pedal, and then the throttle valve is driven to the target throttle opening degree so as to adjust an amount of intake air.
The relation of an intake air volume G.sub.AIR to a throttle opening degree .theta..sub.TH is not in a linear proportional relation but shows a characteristic curve as shown in FIG. 1, and as the throttle opening degree becomes large, the intake air volume is rapidly increased.
Due to such a characteristic of .theta..sub.TH -G.sub.AIR as described above, there occurred problems as follows. If carbon clogs around the throttle valve or in a bypass air passage, it is difficult to keep an amount of variation of the intake air volume G.sub.AIR at a suitable value under the idle state that the throttle valve opening degree .theta..sub.TH is small, because the amount of variation of the intake air volume G.sub.AIR. is quite low in respect to an amount of variation of the throttle opening degree .theta..sub.TH, or an amount of variation of the intake air volume G.sub.AIR is apt to excessively increase in response to ON/OFF of an electrical load E.sub.L of an air conditioner or the like as the throttle opening degree .theta..sub.TH increases at a low engine water temperature or at a low intake absolute pressure (under an idle feed-back control in particular, variation of the rotational speed of the engine (shock) due to the ON/OFF of the electrical load is intense around the target rotational speed of the engine).